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Deferred Policy Acquisition Costs - Narrative (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
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Deferred Policy Acquisition Costs Disclosures [Abstract] |  |
Accumulated amortization of present value of future profits | $ 153 | $ 148

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- Definition The cumulative amount of amortization of present value of future profits that has been recognized in the Income Statement. + References No definition available. + Details
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Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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